The present invention pertains to improvement in bulk material analyzers.
Bulk material analyzers are used to measure the elemental content of bulk material. Such analyzers have been developed primarily to measure the quantitative content of materials, such as ash, in batches of coal, but also are useful for measuring the elemental content of the bulk materials. Such development is described in the following publications: Stewart and Hall, "On Line Monitoring of Major Ash Elements in Coal Conversion Process," Reprint 789671, October 1978, 13th Intersociety Energy Conversion Engineering Conference, Society of Automotive Engineer, Inc. Warrendale, Pa., pp 586-591; Cekorich et al "Development of an Elemental Analyzer for Coal, Oil and Similar Bulk Streams--A Status Report," 1979 Symposium on Instrumentation and Control Fossil Energy Processes, Aug. 20, 1979, Denver, Colo., pp 297-313; Yeager "R & D Status Report, Coal Combustion Systems Division," EPRI journal; June 1981, pp 32-24; Cooper, "Progress in On-Line Coal Quality Measurement," CQ, January 1984, pp 16-23; and NOLA 1 Data Sheet, "Neutron Activation Analysis for Industrial Process Control, Model NA 79," Texas Nuclear Division of Ramsey Engineering Company, Austin, Tex.
In a typical prior art bulk material analyzer, the bulk material is transported through an activation region between a radiation source and a gamma ray detector, and the detector produces signals which are processed to provide a measurement of the elemental content of the bulk material. Typically the radiation source is a neutron source. When the bulk material is bombarded by the radiation, secondary emissions of gamma rays are produced from the bulk material. Different characteristic gamma ray energy spectra are produced from different elements in the bulk materials. Accordingly by processing detected signals that are indicative of the gamma ray spectrum a measurement is provided of the elemental content of the bulk material. This measurement process is known in the art as prompt gamma ray neutron activation analysis (PGNAA).
In the system described by Stewart and Hall, which is also known as the Bureau of Mines system, the bulk material is fed through a hopper into a circular cross-section vertical chute. The radiation source is located within the vertical chute and the detector is located outside the chute at the same level as the radiation source.
In the Bureau of Mines system the strength of the signals produced by the detector is dependent upon the lateral distribution of the bulk material in the chute. Since bulk materials may exhibit gross segregation by particle size and density as they pass through the chute, the distribution of elemental content is generally quite inhomogenous. Thus there is a degree of inaccuracy in the measurements provided by processing the detector-produced signals. Such inaccuracy is proportional to the inhomogenity of the bulk material multiplied by the spatial nonuniformity of the detector response.
In the system described by Cekorich et al, which is known as the MDH system, the bulk material is channeled through the activation region by a relatively small vertical chute having an elongated rectangular cross-section of approximately 10 inches (25 cm) by 14 inches (35 cm); and two radiation sources are symmetrically disposed outside the chute on one of the long sides of the chute, and aligned normal to the long sides of the chute. A single detector is centered outside the other of the long sides of the chute between positions opposing the positions of the sources; and is aligned normal to the long sides of the chute. The symmetrical disposition of the two radiation sources and the detector tends to reduce the dependence of the detector-produced signals upon the lateral distribution of the bulk material within the chute. However, bulk material flow problems, such as plugging, bridging and segregation within the chute, occur in the MDH system, whereby particle top-size generally is limited to very dry particles that can pass through a minus two-inch (5 cm) mesh. As a result bulk materials such as coal must be crushed before they can be transported through the MDH system. The flow rate for coal is limited by the chute size to approximately thirty tons (27,000 Kg) per hour in the MDH system.
Bulk material analyzers typically are used at the bulk material processing or utilizing facilities. Knowledge of the elemental content is important to determining those operating parameters which will provide optimum material processing. For example, coal analysis enables knowledgeable blending of batches of coal having excessive ash and sulfur content with batches of a coal having lower contents of ash and sulfur. In the prior art of coal processing several discontinuous elemental-content measurements are made for each batch of coal. These measurements are averaged to provide an averaged weighted measurement. Using conventional ASTM sampling and analysis techniques, the desired information typically is not available for several hours.
In prior art on-line coal analyzers, the radiation source and the detector assembly are located around a chute or a conveyor and integrated into a permanent structure at the power plant. The signal processing equipment must be located in a separate enclosure or building in order to protect such equipment from dust and adverse local environmental conditions.
In summary, the prior art systems utilize various separate components and subassemblies that are installed in separate buildings or enclosures. Such systems are expensive to install and may be difficult to maintain. They also may require a large amount of space and expensive electrical cable interconnections between the separate buildings.